Assessment of left ventricular function at rest and analysis of arrhythmias prior to hospital discharge allows prediction of a portion of the 10-15% of patients who will die suddenly within six months of discharge after acute myocardial infarction. Using new non-invasive radionuclide cineangiographic techniques, which permit study during exercise and hence provide more complete assessment of cardiac function than previously available, we found that prediction of death within a year after infarction was not improved by assessment during exercise. However, though no significant change in left ventricular function occurred in the group during the course of the year after infarction, assessment of function during exercise did permit selection of a subgroup of patients manifesting significant functional improvement.